In general, a front exterior casing for an electronic apparatus, such as a portable telephone or a smart telephone, has a structure in which a front exterior casing on the front side and a front exterior casing on the back side, made from a synthetic resin material, are combined with each other. Onto a surface of the front exterior casing on the front side, a protective panel is secured by a fusion-bonding process or the like, so as to protect a liquid crystal display window. As the protective panel, conventionally, a colorless transparent resin panel has been used; however, together with recent demands for fashionable electronic apparatuses, a decorative pattern such as rimming has been applied thereto by a printing process.
In recent years, in the field of portable telephones, a portable telephone provided with an input device function on a protective panel, as shown FIG. 12, has been highly expected as the next interface, and, for example, Patent Document 1 has disclosed such a telephone.
Referring to an exploded view of FIG. 13, the following description will discuss a protective panel 100 with a touch input function of an electronic apparatus display window in detail. In FIG. 13, the protective panel 100 with a touch panel function of an electronic apparatus display window is provided with a lower electrode panel 103 that has a lower transparent electrode 105 and lower circuits 107a and 107b installed on a periphery of the lower transparent electrode 105, which are placed on an upper surface of a protective panel main body, and an upper electrode 102a that has an upper transparent electrode 104 placed at a position opposed to the lower transparent electrode 105 on a lower surface of a transparent insulating sheet, and upper circuits 106a to 106d, and 107c and 107d, installed on a periphery of the upper transparent electrode 104, and is also provided with an upper electrode sheet 102a that is bonded to the lower electrode panel 103 at a peripheral edge portion so as to form an air cell between the transparent electrodes 104 and 105, and a decorative sheet 102b having a decorative layer 117 that is formed on a periphery of a transparent window portion 118 in a frame shape on at least one of the surfaces of the transparent insulating sheet so as to cover the lower circuits 107a and 107b and the upper circuits 106a to 106d and 107c and 107d, with the decorative sheet 102b bonded to an upper surface of the upper electrode sheet 102a. 
The protective panel 100 with a touch input function having this structure is designed so that, when pressed at a point on a surface of the decorative sheet 102b thereof by a finger, or a pen, or the like, the decorative sheet 102b is warped centered on the pressed point integrally with the upper electrode sheet 102a (hereinafter, a laminated member of the upper electrode sheet 102a and the decorative sheet 102b is referred to as a movable sheet 102), with the result that respective transparent electrodes 104 and 105, formed on the inner surfaces of the upper electrode sheet 102a and the lower electrode panel 103, are made in contact with each other so that an input position is detected.
FIGS. 14A and 14B are cross-sectional views that show one example of a mounted structure in the front exterior casing, which uses the protective panel with a touch input function. As shown in FIGS. 14A and 14B, the front exterior casing 119 is provided with a panel fit-in portion 122 to which the protective panel 100 with a touch input function is fitted. The panel fit-in portion 122 is designed so that its depth is substantially equal to the thickness dimension of the protective panel 100 with a touch input function so as to form a seamless structure in which an outer surface of the protective panel 100 is allowed to form the same plane as its peripheral portion. Moreover, on a bottom surface of the panel fit-in portion 122, an opening or a concave section 123 that is slightly smaller than the bottom surface is formed for a display device 120 to be placed therein so as to be visually recognized from the outside through the protective panel with a touch input function, and on a peripheral edge 122a of the bottom surface, the protective panel 100 with a touch input function is supported, and is secured with an adhesive or a double-sided tape 124.
In this case, with respect to the frame area covered with the decorative layer of the upper electrode sheet 102a, the thicknesses of a portion where the upper circuits 106a to 106d, and 107c and 107d are formed and another portion where no circuits are formed are different from each other by the corresponding circuit portion. In an attempt to bond this to the lower electrode panel at peripheral edge portions by using a paste layer, a lower surface of the base member of the portion where no circuits are formed of the upper electrode sheet 102a needs to be pressed down to a level lower than a lower surface of the base member of the portion where the circuits are formed, and then bonded thereto. Since the paste layer 130 (see FIG. 16) is formed on the entire portion of a peripheral edge of the upper electrode sheet 102a, an abrupt deformation occurs in the base member of the upper electrode sheet 102a along the border between the portion where the circuits are formed and the other portion where no circuits are formed. As a result, since the entire movable sheet 102 is formed as a comparatively thin sheet having flexibility, a step (for example, a step of about 20 μm when the circuit thickness is about 10 μm), referred to as a sink mark 132 caused by the presence or absence of the circuit formation, is stood out, when a surface of the movable sheet 102 is viewed (see FIG. 16). The presence of this sink mark 132 on the decorative layer portion causes degradation of the outside appearance and is not desirable.
In order to avoid this sink mark, as shown in FIG. 15, a structure has been proposed (see Patent Document 2) in which, with respect to the upper electrode sheet 102a, the upper circuits 106a to 106d, and 107c and 107d are formed on the frame area corresponding to the upper transparent electrode 104 and the periphery of the upper transparent electrode 104 located on a lower surface of the transparent insulating sheet, and on a portion within the frame area where the upper circuits 106a to 106d, and 107c and 107d are not formed, a dummy circuit 125 used for adjusting the thickness is formed with substantially the same thickness as that of the upper circuits 106a to 106d, and 107c and 107d, in a manner so as not to cause a short circuit.